Why does this Ext.grid.Panel crash? - extjs4

Question

This crashes:
var grdMakes = Ext.extend(Ext.grid.Panel, {
constructor: function(paConfig) {
}
}
This does not:
var grdMakes = Ext.extend(Ext.grid.Panel, {
}
The crash is:
Uncaught TypeError: Cannot read property 'added' of undefined
Why does adding a constructor cause it to crash? I can do it with other objects like:
var pnlMakesMaint = Ext.extend(Ext.Panel, {
constructor: function(paConfig) {
}
} // just fine
EDIT
To clarify what I want to do is that I want to be able to instantiate an object with the option to override the defaults.
var g = new grdMakes({}); // defaults used
var g = new grdMakes({renderTo: Ext.getBody()}); // renderTo overridden
This is working for everything except the Ext.grid.Panel
Also, I'm using ExtJS 4
SOLUTION
Turns out, extend is deprecated in ExtJS 4. So I used this and it works:
Ext.define('grdMakes', {
extend: 'Ext.grid.Panel',
constructor: function(paConfig) {
var paConfig = Ext.apply(paConfig || {}, {
columns: !paConfig.columns ? [{
header: 'Makes',
dataIndex: 'make'
}, {
header: 'Description',
dataIndex: 'description'
}]: paConfig.columns,
height: !paConfig.height ? 400 : paConfig.height,
renderTo: !paConfig.renderTo ? Ext.getBody() : paConfig.renderTo,
store: !paConfig.store ? stoMakes : paConfig.store,
title: !paConfig.title ? 'Makes' : paConfig.title,
width: !paConfig.width ? 600 : paConfig.width
});
grdMakes.superclass.constructor.call(this, paConfig);
}
}

Answer 1

Ok.But your code seems like ExtJS3.Because Ext.extend is depreceated in ExtJS4 version.Instead of extend you can use define.For reference you can check the following url:
http://docs.sencha.com/ext-js/4-0/#/api/Ext-method-extend
Afaik,for overriding default options,this is not the perfect way.You need to use Ext.override.
For example:
Ext.override(Ext.grid.Panel,{
lockable : true
});
Like above you have to override the default options.